{
 "cells": [
  {
   "cell_type": "code",
   "execution_count": 16,
   "metadata": {},
   "outputs": [],
   "source": [
    "class Solution(object):\n",
    "    def arrangeCoins(self, n):\n",
    "        \"\"\"\n",
    "        :type n: int\n",
    "        :rtype: int\n",
    "        \"\"\"\n",
    "        left = 1\n",
    "        right = n\n",
    "        while left <= right:\n",
    "            mid = (left + right) // 2\n",
    "            stair = mid * (mid + 1) // 2\n",
    "            if stair == n:\n",
    "                return mid\n",
    "            elif stair > n:\n",
    "                right = mid - 1\n",
    "            else:\n",
    "                left = mid + 1\n",
    "        return right"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 17,
   "metadata": {},
   "outputs": [],
   "source": [
    "s = Solution()"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 18,
   "metadata": {},
   "outputs": [
    {
     "data": {
      "text/plain": [
       "0"
      ]
     },
     "execution_count": 18,
     "metadata": {},
     "output_type": "execute_result"
    }
   ],
   "source": [
    "s.arrangeCoins(0)"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": null,
   "metadata": {},
   "outputs": [],
   "source": []
  }
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